Built Head Questions
i did post what was in the pm.
i am going to have my spare head built and the combustion chamber is going to be reworked ( had small chips in it when a ring land broke) so therorically that should help compensate and make the quench area larger ( closer to where it was before the mill work was done)
i am going to have my spare head built and the combustion chamber is going to be reworked ( had small chips in it when a ring land broke) so therorically that should help compensate and make the quench area larger ( closer to where it was before the mill work was done)
Thread Starter
Evolved Member
iTrader: (25)
Joined: Feb 2005
Posts: 1,607
Likes: 0
From: Upstate, SC
the quench area is the section of the head that is domed and the area left below the deck of the block and above the piston top. plus the area that the head gasket bore creates and the area between the side of the piston and the block above the compression rings.
when i milled the head and block i decreased the quench area causing the combustion gases to increase in temp. if i removed material from the combustion chamber dome i should reincrease the quench area.
when i milled the head and block i decreased the quench area causing the combustion gases to increase in temp. if i removed material from the combustion chamber dome i should reincrease the quench area.
If it was my head and I was using it on a street engine, not a full out race motor, then I donīt see the advantage of a 1mm increase in valve diameter. Thatīs pretty dinky and shouldnīt make any difference in a high velocity(as opposed to high volume) port job. If the stock valves are in good shape then I would just reuse with a good valve job. But if you want to spend more money then go ahead and get the 1mm larger valves.
Sure, but you can have the head ported w/o purchasing new valves. Why buy new valves if you donīt need it. 1mm larger isnīt going to give you anymore HP.
In the old days, most all of my bikes and car heads when ported I just reused the old valves and had a 3-angle valve job done. But, I guess that this is frowned on nowadays. New valves if not needed are not going to produce more power by themselves. If the exhaust valves arenīt burnt then why throw them away?
In the old days, most all of my bikes and car heads when ported I just reused the old valves and had a 3-angle valve job done. But, I guess that this is frowned on nowadays. New valves if not needed are not going to produce more power by themselves. If the exhaust valves arenīt burnt then why throw them away?
Last edited by sparky; Apr 16, 2008 at 08:45 PM.
the quench area is the section of the head that is domed and the area left below the deck of the block and above the piston top. plus the area that the head gasket bore creates and the area between the side of the piston and the block above the compression rings.
when i milled the head and block i decreased the quench area causing the combustion gases to increase in temp. if i removed material from the combustion chamber dome i should reincrease the quench area.
when i milled the head and block i decreased the quench area causing the combustion gases to increase in temp. if i removed material from the combustion chamber dome i should reincrease the quench area.
I would worry more about who is going to do the porting, than what difference 1mm larger valves are going to make. FWIW, 1mm in valve diameter isnīt going to make any measurable difference on a velocity port job. I donīt think that youīll find any comparative flowbench data regarding a 1mm variance in valve size in an Evo head either(I am usually wrong though).
Last edited by sparky; Apr 16, 2008 at 09:19 PM.
Oh, and as for valves, when buschur first started flowing the EVO head and port testing, I believe he got a 12% increase in flow on the intake.
Found the thread:
The oversized valves do ALOT.
Found the thread:
Originally Posted by davidbuschur
Oh brother! I got the head back today, HOLY CRAP does this thing flow with the new valves in it. I am absolutely stunned at the results.
The only thing that I don't like is the guy that flowed the head used a pipe on the exhaust port. I don't like doing this. What it does is straightens out the airflow at the end of the port. The CFM, as far as I know, always increases. He didn't flow the exhaust without the pipe which is useless as all the other tests were done without it. I will have to have the exhaust port flowed again.
The results below are the percentage over stock.
Check this out.
Intake mild porting stk valves additional porting large valves
lift
.100 4% 27%
.200 1% 19%
.300 4% 14%
.400 9% 19%
.500 8% 20%
The only thing that I don't like is the guy that flowed the head used a pipe on the exhaust port. I don't like doing this. What it does is straightens out the airflow at the end of the port. The CFM, as far as I know, always increases. He didn't flow the exhaust without the pipe which is useless as all the other tests were done without it. I will have to have the exhaust port flowed again.
The results below are the percentage over stock.
Check this out.
Intake mild porting stk valves additional porting large valves
lift
.100 4% 27%
.200 1% 19%
.300 4% 14%
.400 9% 19%
.500 8% 20%
Mr. Buschur seemed to believe that the gains were mostly due to the valves, but perhaps he just wanted to sell more parts.
Send me a head with at least one good intake port two stock size valves and two 1mm over valves and I'd be happy to put it on a flow bench and let you all know what I get.
Just for reference, it's a combined valve size of .080 over, and comparing apples to oranges, I've seen production casting LS heads go all the way to 370 with .100 over valve.
Send me a head with at least one good intake port two stock size valves and two 1mm over valves and I'd be happy to put it on a flow bench and let you all know what I get.
Just for reference, it's a combined valve size of .080 over, and comparing apples to oranges, I've seen production casting LS heads go all the way to 370 with .100 over valve.
Last edited by icantdrive75; Apr 16, 2008 at 09:46 PM.
Hey I am not arguing with Dave Buschur, or Smokey Yunick for that matter, I am only arguing with you. Itīs just that they are comparing a mildly ported head to a head with "additional" porting.
Or did you find a way to isolate the gain in flow attributable to only the 1mm increase in valve diameter without factoring in the more fully massaged ports, bowls, stems and seats, eventhough you werenīt there that day, or were you?
Or did you find a way to isolate the gain in flow attributable to only the 1mm increase in valve diameter without factoring in the more fully massaged ports, bowls, stems and seats, eventhough you werenīt there that day, or were you?
Last edited by sparky; Apr 16, 2008 at 10:03 PM.
Thread Starter
Evolved Member
iTrader: (25)
Joined: Feb 2005
Posts: 1,607
Likes: 0
From: Upstate, SC
well i think i still have a few stock valves left over from the last time i built the head i am willing to lend out as well as a spare head with virgin ports. but i would need them back. any one have a few spare 1+ mm valves to lend for testing?
It's not just a matter of the valves being larger, but they are shaped differently than the stock ones to increase flow. If you were to compare them side by side you would see that the aftermarket valve has a completely different profile. We spent a lot of time testing all the valves out there to find which ones flowed better and that's what we use. If I get some time this afternoon I'll take some side-by-side photos to show you what I'm talking about. There is also a lot of flow to be found in the valve job. How much time the builder takes to find the right valve angles for that particular head can make a world of difference.
